In a phased array antenna, the radiated energy is directionally concentrated by arranging and combining individual antenna elements (single antennas). When the single antennas can be controlled differently, the antenna pattern of the antennas is electronically pivotable. Directional concentration is all the stronger, the greater the transverse extension of the antenna. In two-dimensional antenna arrays, the antenna pattern can be concentrated in the vertical direction and in the horizontal direction. The antenna pattern also called the radiation pattern) can be asymmetrically controlled by controlling the difference in phase position.
Such an array antenna uses phase shifting among the transmitter elements arranged in a matrix in order to achieve directional concentration by interference. The transmission energy is intensified in the desired direction, whereas the undesired directions are cancelled by destructive interference. The individual antenna elements themselves do not need any devices for concentrating the beam directionally.
If a different phase difference is set, for example by adjusting the phase angle of the outer elements to lag and that of the inner elements to lead, the directional concentration of the antenna as a whole is altered, which means the shape of the antenna pattern changes. To obtain a very narrow antenna pattern, very many antenna elements are needed, with the phase differences between the emitters being added toward the edge of the antenna group. The phase shifters used for phase shifting must thus achieve a phase shift of almost 360°, and that phase shift must be implemented extremely fast. In practice, different delay elements are used that are connected to the feed line, for example in steps of 22.5° in the case of a 4-bit phase shifter with a 16-bit control word. The control word may also contain addressing information.
Linear array antennas are composed of rows that can be jointly controlled by a phase shifter. Phase shifters can be realized, also as delay elements, in a manner known per se. Planar array antennas may be composed of individual elements each with one phase shifter per element. The elements are arranged as in a matrix, the array antenna as a whole being formed by the planar arrangement of all the elements.
Array antennas may be fed via a feed line, in which case the energy is fed in series or in parallel to the antenna elements through coaxial cables, waveguides or other high-frequency feed lines (HF feed lines).
Alternatively, energy may also be fed by a central emitter, i.e., with energy that has already been radiated. These are then radiation-fed array antennas.
A distinction is also made between a series-fed array, in which the radiator elements are supplied consecutively with transmission power and with increasing phase shift through increasingly long feed lines, and parallel-fed arrays, in which each radiator element is supplied through an equally long feed line and therefore with the same phase. In the case of parallel-fed arrays, the length of the feed lines can therefore be ignored when calculating the phase shift.
Phased array antennas thus allow electromagnetic waves to be concentrated and electronically controlled in a specific direction. Such directional radiation is also referred to as beamforming. Beamforming can be used to increase the distance covered by wireless data transmission or by a radar application, and to reduce both interference and multipath propagation. In the case of radar applications, spatial resolution of the radar echo can be achieved with the aid of beamforming.
In order to achieve antenna patterns that are as sharply concentrated as possible, phased array antennas are preferably equipped with a plurality of antenna elements (1024, for example). The phase and amplitude can typically be separately adjustable for each single antenna element, for electronically adjusting the beam direction. As already mentioned, digital control signals are typically guided for that purpose to a plurality of phase shifter circuits (for example, 1024). This distribution of the digital control information requires a plurality of feed lines and therefore a complicated antenna module layout. If necessary, additional layers of metal must be provided for feeding the respective digital signals, as a result of which the production effort is increased.
Documents U.S. Pat. Nos. 5,821,901 and 5,986,590 disclose a phased array antenna in which the control signals are modulated on the same carrier frequency as the useful high-frequency (HF) signals to be transmitted. This involves complex modulation and circuitry to ensure separation between useful signals and control signals.